The vast majority of vehicles currently in use incorporate vehicle communication systems for receiving or transmitting signals. For example, vehicle audio systems provide information and entertainment to many motorists daily. These audio systems typically include an AM/FM radio receiver that receives radio frequency (RF) signals. These RF signals are then processed and rendered as audio output. A vehicle communication system may incorporate other functions, including, but not limited to, wireless data and voice communications, global positioning system (GPS) functionality, and satellite-based digital audio radio services (SDARS). The vehicle communication system may also incorporate remote function access (RFA) capabilities, such as remote keyless entry, remote vehicle starting, seat adjustment, and mirror adjustment.
Communication systems, including vehicle communication systems, typically employ antenna systems including one or more antennas to receive or transmit electromagnetic radiated signals. In general, such antenna systems have predetermined patterns and frequency characteristics. These predetermined characteristics are selected in view of various factors, including, for example, the ideal antenna RF design, physical antenna structure limitations, and mobile environment requirements. Because these factors often compete with each other, the resulting antenna design typically reflects a compromise. For example, an antenna system for use in an automobile or other vehicle preferably operates effectively over several frequency bands (e.g., AM, FM, television, RFA, wireless data and voice communications, GPS, and SDARS), having distinctive narrowband and broadband frequency characteristics and distinctive antenna pattern characteristics within each band. Such antenna systems also preferably are capable of operating effectively in view of the structure of the vehicle body (i.e., a large conducting structure with several aperture openings). The operating characteristics (i.e., transmitting and receiving characteristics) of such antenna systems preferably are independent of the vehicle body style, orientation, and weather conditions. To accommodate these design considerations, a conventional vehicle antenna system can use several independent antenna systems and still only marginally satisfy basic design specifications.
Significant improvement in mobile antenna performance can be achieved using an antenna that can alter its RF characteristics in response to changing electrical and physical conditions. One type of antenna system that has been proposed to achieve this objective is known as a self-structuring antenna (SSA) system. An example of a conventional SSA system is disclosed in U.S. Pat. No. 6,175,723, entitled “SELF-STRUCTURING ANTENNA SYSTEM WITH A SWITCHABLE ANTENNA ARRAY AND AN OPTIMIZING CONTROLLER,” to Rothwell III (“the '723 patent”). The SSA system disclosed in the '723 patent employs antenna elements that can be electrically connected to one another via a series of switches to adjust the RF characteristics of the SSA system as a function of the communication application or applications and the operating environment. A feedback signal provides an indication of antenna performance and is provided to a control system, such as a microcontroller or microcomputer, that selectively opens and closes the switches. The control system is programmed to selectively open and close the switches in such a way as to improve antenna optimization and performance.
Conventional SSA systems may employ several switches in a multitude of possible configurations or states. For example, an SSA system that has 24 switches, each of which can be placed in an open state or a closed state, can assume any of 16,777,216 (224) configurations or states. Assuming that selecting a potential switch state, setting the selected switch state, and evaluating the performance of the SSA using the set switch state each takes 1 ms, the total time to investigate all 16,777,216 configurations to select an optimal configuration is 50,331.6 seconds, or approximately 13.98 hours. During this time, the SSA system loses acceptable signal reception.
The search time associated with selecting a switch configuration may be improved by limiting the number of configurations that may be selected. For example, if the control system only evaluates 0.001% of the possible switch configurations, the search time can be reduced to slightly less than a second. Laboratory experiments have demonstrated that search times can be made significantly shorter. Nevertheless, the loss of acceptable signal reception every time an SSA system is tuned to a new station, channel, or band is still a significant problem.
Still, known SSA technology is limited to a basic configuration that uses a single point feed system connected to a single port antenna template having a large number of switches. This restriction has a negative impact on its potential performance and flexibility for many applications.